A known type of fluid pressure generating system is disclosed in a new model instruction manual issued on Aug. 27, 1997 for the Toyota Aristo. As described in this instruction manual, the fluid pressure generating system is applied to a brake fluid pressure control system which is adapted to perform anti-slip control, brake assist control, and anti-skidding control.
The fluid pressure generating system includes a fluid reservoir that is adapted to store brake fluid, a fluid pump for generating fluid pressure, and an accumulator for storing pressurized fluid. The accumulator is provided with first and second pressure switches for detecting a pressure value in the fluid circuit. The first pressure switch also controls the operation of the fluid pump. When the first pressure switch detects that the fluid pressure changing value in the accumulator is less than a first predetermined pressure level, the first pressure switch generates a low pressure signal (turn off signal) for the control unit. On the other hand, when the first pressure switch detects that the fluid pressure changing value in the accumulator is more than a second predetermined pressure level which is higher than the first predetermined pressure level, the first pressure switch generates a high pressure signal (turn on signal) for the control unit. When the low pressure signal is generated, the fluid pump is driven and when the high pressure signal is generated, the operation of the fluid pump is suspended after a predetermined period of time.
When the second pressure switch detects that the fluid pressure changing value in the accumulator is less than a third predetermined pressure level which is lower than the first predetermined pressure level, the second pressure switch generates a low pressure signal (turn off signal) to the control unit. On the other hand, when the second pressure switch detects that the fluid pressure changing value in the accumulator is more than a fourth predetermined pressure level which is higher than the third predetermined pressure level, the second pressure switch generates a high pressure signal (turn on signal) to the control unit. When the second pressure switch generates the low pressure signal, the controller determines a disabled condition of the accumulator and turns on a warning lamp and outputs a buzzer using a warning buzzer to alert the operator.
However, this known fluid pressure generating system suffers from certain disadvantages and drawbacks. If the vehicle maintains a parked condition for a long period of time, the stored brake fluid in the accumulator may be leaked. If the leakage from the accumulator is to be eliminated, the accumulator should be designed to ensure an accurate fluid-tight structure. However, it has been found to be rather costly to ensure an accurate fluid-tight manner in the brake fluid circuit. In this known fluid circuit structure, when the engine is turned on after a long term parking condition, the fluid pressure value in the accumulator indicates that the pressure is below the third predetermined pressure level.
In the known system, when the second pressure switch generates a low pressure signal (in another words, when the fluid pressure value in the accumulator is indicated to be below the third predetermined pressure level), the system determines the disabled condition of the accumulator and starts operating the warning system under the non disabled condition of the accumulator. This misoperation especially occurs after long term parking and gives the operator an unpleasant feeling.
In light of the foregoing, a need exists for an improved hydraulic pressure generating system that is not as susceptible to the same disadvantages and drawbacks as the system described above.
It would thus be desirable to provide a hydraulic pressure generating system that is not as susceptible to misoperation such as after long term parking of the vehicle.